Bug 854413 - [MMS][SMS] Move all DOM element property initialization into init methods and rationalize variable names and ids r=julienw

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>
(cherry picked from commit 5a45368a71fc0569bf4adaf8cbf03d4062c6b756)

Conflicts:
	apps/sms/js/message_manager.js
	apps/sms/js/thread_list_ui.js
	apps/sms/js/thread_ui.js